无法使用SharedPreference变量

Question

I'm trying to save and retrieve data with SharedPreferences.
Data stores and retrieved correctly, the problem is the app crashes on using this data to change a button text in a fragment

onCreateView() Function

    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        SharedPreferences loadSettings = getActivity().getSharedPreferences("app_setts", Context.MODE_PRIVATE);
        Button counterBtn = (Button) getActivity().findViewById(R.id.counterBtn);
        int countInt = loadSettings.getInt("counter",0);
        counterBtn.setText(String.valueOf(countInt));

        View rootView = inflater.inflate(R.layout.fragment_main, container, false);
        return rootView;
    }

So how to change the switch values using SharedPreference
*I have searched here but all gives crash
Sorry for bad english

Edit
I have found that i couldn't access the fragment component directly by onCreate() in MainActivity.java so i have to put my code in onCreateView() function

But there is a problem
The app runs and didn't crash but the value still won't change
Any idea to solve this ??

Answer 1

Logcat trace shows the 62nd line throws a NPE.

boolean onoffSwitch = loadSettings.getBoolean("appOnOff", false);

So, loadSettings must be null. You can print this by:

System.out.print(loadSettings);

So, you must try:

SharedPreferences loadSettings = getSharedPreferences("pref", Context.MODE_PRIVATE);
...
loadSettings.commit();

Answer 2

You may be try to get the shared preference value before save. First check you saving the values in shared preference..

Answer 3

There's a couple of issues here.

The first is that you should probably move the code from your fragment's onCreateView() to onActivityCreated(), as that's when you are guaranteed that the Activity's onCreate has completed.

The second issue is that while this may work, it's poor design to have a fragment reach into and manipulate it's parent activity directly in this way.

The Android developer site has a good article about how to communicate between a fragment and it's activity via interfaces, at http://developer.android.com/training/basics/fragments/communicating.html

Personally, I prefer to decouple things even more, forego the interface, and use a message bus (eg Otto, EventBus, etc.) In this way, fragments are completely reusable / replaceable, and neither the activity nor the fragment need to know anything specific about each other - just which bus messages they emit / consume.